Impatiensjenjittikuliae (Balsaminaceae), a new species from Thailand

Abstract Impatiensjenjittikuliae Ruchis. & Suksathan, a new species from a limestone area in Thasongyang District, Tak Province, Northern Thailand, is described and illustrated. This endemic new species is distinguished from the most similar, I.lacei Hook.f. through having pilose lateral sepals vs glabrous, and by the absence of long hairs along the lamina margin. Its pollen and seed morphology, stem anatomy, and pollination ecology are also observed. Furthermore, its conservation status as Critically Endangered is also assessed.

In Thailand, sixty-one native Impatiens species have been enumerated in previous works (Shimizu 1970(Shimizu , 1977(Shimizu , 1991(Shimizu , 2000Shimizu and Suksathan 2004;Suksathan and Triboun 2009;Ruchisansakun et al. 2014). In 2017, the first author cited here noticed an unnamed Impatiens from Tak Province via Weerayuth Laohajinda's Facebook and later on traveled to examine the plant in 2018. After a detailed study, it turned out to be a species new to science. It is therefore described here.
Phenology. Flowering from Oct. to Nov.; fruiting Oct. from Nov. Distribution. The new species is only known from the type locality in Tak Province, Thailand.  Ecology. Impatiens jenjittikuliae grows on limestone close to waterfall in a mixed deciduous forest, 520-600 m elevation (pers. obs.).
Proposed IUCN conservation assessment. Critically Endangered B1ab (i, ii, iii) + 2ab (i, ii, iii). This species is only known from the type locality; the extent of occurrence is estimated to be less than 5 km, where it occurs as a small population (IUCN 2012).
Etymology. The new species is named in honor of Dr. Thaya Jenjittikul who encouraged the first author to step in and study this lovely plant family.
Pollination ecology. The author observed five visitations by bees from the family Apidae (identified by an entomologist, Pornpimon Tangtorwongsakul) during the expeditions. The size of bee body fit well with the floral entrance (Fig. 6). Moreover, the floral structure of this new species is similar to other bee-pollinated species, e.g. I. psittacina (Ruchisansakun et al. 2016). Hence, we concluded that it is a bee-pollinated species.

Discussion
Impatiens jenjittikuliae is similar to I. lacei and the other species closely related to I. pulchra Hook.f (= I. mengtszeana Hook.f. in Ruchisansakun et al. 2015) in its raceme inflorescence, shape of flower, and short fusiform capsule. The short fusiform capsule and the 4-colpate pollen grains of the new species support its placement in the subgenus Impatiens (Yu et al. 2015). In addition, I. jenjittikuliae has seeds coated with inflated cells with granulate walls similar to those described in species, such as I. napoensis Y. L. Chen, within the sect. Uniflorae Yu et al. 2015).
The cross sections of the stem of I. jenjittikuliae have shown that the new species is herbaceous, similar to the morphologically similar species in the sect. Uniflorae, I. pulchra, which also show in Lens et al. (2012) as I. mengtszeana Hook.f. (Lens et al. 2012;Ruchisansakun et al. 2015;Yu et al. 2015).